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[[image: B&W print captioned Early eight-cylinder vee-type engine developed by Renault firm in France]] [[image: B&W print captioned Three-cylinder, air-cooled Anzani was the first truly successful radial engine]] Matthews Manly, the Cornell University-trained engineer, has been called the outstanding genius of early aviation powerplant design. Certainly, the task he undertook was enormously difficult. When he started, he had very little to work with. There may have been the germ of the idea for a rotary engine in the unsuccessful efforts of S. M. Balzer of New York to build an engine for Langley, but it remained for Manly to solve the seemingly endless problems of design and construction. Manly's engine was a 4-cycle, 5-cylinder radial with a bore of 5 in. and a stroke of 5 1/2 in. The cylinders were 1/16 in. thick, made from steel spun from a flat plate. Into them was shrunk a cast-iron liner of the same thickness. The form of construction was novel; Washington machine shops said flatly it was impossible to do the job, so Manly had to show them how. The five cylinders were mounted on a steel, barrel-shaped crank case. The pistons were of cast iron, of lighter weight and more sophisticated design than would become general for years ahead. Everything had to be made specially - the ignition system, the carburetor, even the spark plugs. How well Manly succeeded in this project may be seen in its weight; dry, it was only 125 lb., and with all accessories and cooling water, only 207.5 lb. During three runs, nonstop for 10 hours each time, it produced a constant 52.4 hp. at 950 rpm. This engine, the first of the "modern" aircraft powerplants - a type which after World War I was to be widely used - is not on permanent display at the Smithsonian Institution. The way Wilbur and Orville Wright solved their power-plant problem was much different. The fact that they were satisfied to build what was essentially a lightened adaptation of the conventional 4-cylinder automobile engine of their day is not to be considered a reflection upon their abilities. Quite properly, they felt that solution of the aerodynamic and control problems of the airplane was of paramount importance, and that all they needed in an engine was sufficient power and yet light weight and strength, to get them into the air. Their first engine weighed more than four times as much, per horsepower, as Manly's. How right they were in their reasoning was demonstrated December 17, 1903. Although their water-cooled engine, with its 4-in. bore and stroke, generally followed automobile practice, the Wrights did not hesitate to make the major design modifications they felt necessary. For example, they positioned the four cylinders horizontally, with the automatic inlet valve located over the exhaust valve. Fuel was fed by gravity to a tube leading through the water jacket where it was vaporized, and then into the inlet manifold where it was mixed with the incoming air. The cylinders and pistons were made of cast iron, the crankshaft machine steel, and the crankcase and water jacket cast aluminum alloy. The Wrights' first engine weighed about 200 lb., including all accessories and cooling water, and produced 12 hp. at 1,090 rpm. By 1906, they had overcome earlier heating troubles. Other improvements included better machining of the cylinders and pistons, and addition of a fuel pump. Now they could hold power output at 25 hp. at 1,300 rpm. (the 1903 engine output dropped by almost 25 per cent after running a few minutes). Not long after, the Wright brothers began building engines producing up to 40 hp. Their four cylinders were now vertical on an aluminum crank-case. Fuel was fed by injection into the inlet port of each cylinder. Beginning 1912-13, the built a 6-cylinder vertical engine rated at 60 hp.; both fuel injection and carburetion were available. Wilbur and Orville Wright constructed about 100 4-cylinder and about 50 6-cylinder power plants. Generally conventional, their engines showed consistent improvement over the years, and reflected the philosophy of the brothers that reliability rather than lightness was what was most important. A 1910 compilation of aviation engines showed about 76 types being constructed in Europe and the United States. Of these, 22 were 4-cylinder verticals and two were 6-cylinder verticals. The 4-cylinder engines of that day did not produce the evenness of torque desired when directly connected propellers were used and flywheels eliminated; demands for greater power also made necessary an increase in the number of cylinders. By 1912, a list of engines numbered 112 types, of which 42 were verticals, 24, 4-cylinder, and 16, 6-cylinder. By the beginning of World War I, most of the vertical engines for aviation use were 6- or 8-cylinder designs. Among American manufacturers of this type were Curtiss, Sturtevant, Kirkham, Christofferson, Aeromarine, Duesenberg, Wisconsin, Maximotor, Hall-Scott and Elbridge. An early improvement over the vertical type in the layout of aviation powerplants was the vee engine. Power could be as much as doubled with, at most, only a slight increase in crankshaft length. The early vee-type engine usually had 8 cylinders, although others manufactured with 16 and even 32 cylinders. More even torque was transferred to the propeller than could be done by the upright engines, and designers found it easier to reduce crankshaft vibration. A vee-type engine that enjoyed great popularity in French aviation for several years beginning about 1908 was the Antoinette, designed by Leon Levasseur. Somewhat earlier, he had built engines rated up to 8 hp. for use in motorboat racing. His best known aviation engines were rated at 50 hp. and had 8 cylinders. The Page 12
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